Optional to return "one or the other"

Question

In Spring JPA, I have two repositories like so,

public interface RepoA extends .... {
  Optional<A> findByDomain(String domain);
}

public interface RepoB extends .... {
  Optional<B> findByHost(String host);
}

And in my service implementation I would like to first check if theres anything returned by RepoA. If there is then convert to a DTO. Otherwise I would like to check if there is anything returned by RepoB and again convert it to a DTO. If nothing is being returned by either repositories then return essentially a null. So using Optional I implemented the service like below,

public class ServiceImpl ... {

  private RepoA repoA;
  private RepoB repoB;

  private Mapper mapper;

  private BDTO findByHost(String domain) {
    return Optional.ofNullable(domain)
              .flatMap(repoB::findByHost)
              .map(t -> mapper.B_To_BDTO(t))
              .orElse(null);
  }

  public Optional<BDTO> findByDomainOrHost(String domain) {
    return Optional.of(Optional.ofNullable(domain)
              .flatMap(repoA::findByDomain)
              .map(i -> mapper.B_To_BDTO(i.getTransport()))
              .orElseGet(() -> findByHost(domain)));

  }
}

So what I'm trying to do is return a Optional<BDTO> which could either be a mapped result of either repoA::findByDomain or repoB::findByHost. Is there another "nicer" way to achieve this using Optional ?